A battery mounted in a vehicle has an output capability decreased in a low-temperature environment. Accordingly, a configuration for heating the battery using a heater has been proposed. For example, in Patent Literature 1, a comb-shaped electrode is formed on a flexible PET resin substrate, and a resin PTC heating element is applied and formed on the comb-shaped electrode, thus forming a sheet heating element. Further, the sheet heating element is wound around the periphery of four sides of a battery mounted in a vehicle, and current is conducted to the comb-shaped electrode, thus heating the battery.